1. Field of the Invention
The present invention relates to an electrically operated chucking apparatus which includes an electrically operated actuator as s drive source and which is constructed to hold an object, such as an electric or electronic component or any other member or part.
2. Discussion of Related Art
For holding or chucking an electric or electronic component, member or part, or any other object, there is known an electrically operated chuck driven by an electrically operated actuator. In an electric-component mounting system arranged to mount electric components on a printed-wiring board or other circuit substrate, for example, such an electrically operated chuck is used by a component-mounting head operable to hold the electric component and transfer the electric component onto the board.
The electrically operated chuck is required to hold the object with high operating stability. To this end, the chuck is desirably arranged to be able to produce a sufficiently large chucking or holding force. Where the object to be held by the chuck is an electric component or any other comparatively brittle member or part, however, the holding force should not be excessively large, and should be controlled to an optimum value to assure stable holding of the object. Further, where the object is held by the chuck with a predetermined constant operating stroke of chucking jaws, a variation in the dimension of a gripping portion of the object at which the object is held will cause a variation in the holding force applied to the object, leading to a problem of deteriorated operating stability of the chuck.
One considered solution to the problem indicated above is to interpose an elastic body such as a rubber member or a sheet spring between the gripping portion of the chuck and the gripping portion of the object. The elastic member is expected to control the holding force owing to its elasticity or elastic deformation. To reduce the amount of variation in the holding force of the chuck according to this solution, it is required to reduce the spring constant of the elastic body as much as possible. To meet this requirement, however, the required operating stoke of the chucking jaws of the chuck is inevitably increased, resulting in an undesirable increase in the size of the chuck, which is a problem in the field of technology in which space reduction is desired in designing an assembly or equipment including the electrically operated chuck. In addition, a decrease in the spring constant of the elastic body tends to deteriorate the accuracy of positioning of the object by the chuck when the chuck is opened to release the object. Namely, the resiliency of the elastic body may displace the object once positioned by the closed chuck. In this respect, the chuck using an elastic body is not suitable in the field of art requiring a high degree of positioning accuracy of the object.